The invention relates to a method of storing character data in a background memory of a digitally operable data display apparatus for displaying as an entity on a screen of a display device a quantity of data which is represented by digital codes stored in a display memory, the displayed data being in the form of discrete pixels or dots, each of which has its colour and/or luminance defined by a respective digital code in the display memory at a location corresponding to the position of the pixel in the display, the apparatus including a processor for controlling digitally the storage, selection and display of data.
The invention further relates to a method of displaying data in a digitally operable data display apparatus for displaying as an entity on a screen of a display device a quantity of data which is represented by digital codes stored in a display memory, the displayed data being in the form of discrete pixels or dots, each of which has its colour and/or luminance defined by a respective digital code in the display memory at a location corresponding to the position of the pixel in the display, the apparatus including a processor for controlling digitally the storage, selection and display of data.
This invention still further relates to digitally operable data display apparatus for displaying as an entity on a screen of a display device a quantity of data which is represented by digital codes stored in a display memory, the displayed data being in the form of discrete pixels or dots, each of which has its colour and/or luminance defined by a respective digital code in the display memory at a location corresponding to the position of the pixel in the display, the apparatus including a processor for controlling digitally the storage, selection and display of data.
The display produced by apparatus of the above type is termed a bit-map display, and is, for example, a 320.times.250 resolution dot matrix colour display which may be displayed on the screen of a CRT (cathode ray tube) or other display device. In the case of a raster scan display device the digital codes stored in the display memory are accessed repeatedly by the processor to update the display in a recurrent cycle of scanning lines which may be produced with or without interlaced field scanning.
Where a data display apparatus of the above type is to provide comprehensive and visually aesthetic text displays, it is usually a requirement that data for a large number of different character fonts is provided in a background memory and the data for individual characters selected for display is read from the background memory and written into the display memory.
It is known to store the data for each character of each character font in a bit-map form which corresponds to the image and size of the character shape. This character data, when selected, can then be transferred directly to the display memory with a minimum of processor logic.
With the known techniques the speed of transfer of the data from the background memory to the display memory is limited due to the relatively large number of processor instructions needed to effect the transfer.